Fixing device especially for a transversal bar on an automobile roof

The system for mounting a cross-bar (2) on a car roof (1) comprises slides (5a, 5b) with hooked ends (510, 520). These fit into grooves (3a, 3b) in the roof. The slides are mounted in converging guide rails (4a, 4b) and are locked in position by a nut (612) and bolt (611) passing though a bar (610) which connects their upper ends.